The invention relates to extraction towers, more specifically, to such towers as are used in the production of sugar for the leaching of sugar beet cossettes or comminuted sugar cane in a counter-current flow of leaching liquid. Such towers are conventionally provided with a tower housing and a rotatably supported center shaft in the tower, which is connected to drive means for rotating the center shaft. Feed advance elements in the form of wings and/or worm screws are secured to the rotatable center shaft and spaced from each other along the length of the shaft to provide spacings between adjacent feed advance elements. It is also known to use baffle plates in such towers which reach into the spacings between adjacent feed advance elements. Such baffle plates act as guide plates for the material being leached.
Various embodiments of the just described basic structure are well known in the art, whereby the mentioned guide plates or baffle plates reach radially inwardly from the tower housing. In other words, the baffle plates have a free end pointing toward the central shaft and an opposite end rigidly or rotatably secured to the inner wall of the tower housing. Reference is made in this connection to German Pat. 1,017,549. The guide or baffle plates also have a certain slant of inclination relative to the horizontal in order to cooperate with the feed advance elements of the driven central shaft or the tower in advancing the material to be leached in counter-current fashion through the tower. This cooperation between the feed advance elements of the central shaft and the baffle plates assures a repeated turn-over of the material being leached. Such repeated turn-over or turning of the material is important because it results in an improved, more intensive contact between the material being leached and the leaching liquid. Another advantage of these guide or baffle plates is seen in that they contribute to avoid jamming of the material in the tower since the plates act as guide means which facilitate determining the flow direction of the material being leached.
Conventional extraction towers with the radially inwardly directed guide plates require a relatively strong tower housing construction because the radially outwardly extending ends of the guide plates are secured to the tower wall and the wall must be accordingly rather thick. The tower wall must not only take up the pressure created by the material in the tower, but also those forces must be taken up by the tower wall, which are transmitted from the guide plates into the tower wall. As a result, prior art tower housings require a substantial quantity of material, especially steel and the tower housings are very heavy so that their transport and the assembly of individual tower sections becomes difficult and expensive.